The present invention relates to organic light emitting devices. In particular, the present invention relates to a stacked organic light emitting device having high brightness and high efficiency.
Organic light emitting devices (xe2x80x9cOLEDsxe2x80x9d) have been known for approximately two decades. All OLEDs work on the same general principles. One or more layers of semiconducting organic material is sandwiched between two electrodes. An electric current is applied to the device, causing negatively charged electrons to move into the organic material(s) from the cathode. Positive charges, typically referred to as holes, move in from the anode. The positive and negative charges meet in the center layers (i.e., the semiconducting organic material), combine, and produce photons. The wave-lengthxe2x80x94and consequently the colorxe2x80x94of the photons depends on the electronic properties of the organic material in which the photons are generated.
The color of light emitted from the organic light emitting device can be controlled by the selection of the organic material. White light is produced by generating blue, red and green lights simultaneously. Specifically, the precisely color of light emitted by a particular structure can be controlled both by selection of the organic material, as well as by selection of dopants.
Organic light emitting devices have been shown to be capable of emitting with very high brightnesses ( greater than 105 cd/m2) and with high quantum efficiencies (2-3%). Unfortunately, the highest brightnesses are achieved with a proportionate reciprocal decrease in lifetime of the device. Also, when power efficiency is considered, operating an OLED at high brightness (and therefore high current) leads to a reduction of power efficiency, as the devices have a significant series resistance, so that the power efficiency drops with increasing current density.
Although substantial progress has been made in the development of OLEDs to date, substantial additional challenges remain. For example, the class of devices continues to face a general series of problems associated with their long-term stability. In particular, the sublimed organic film may undergo recrystallization or other structural changes that adversely effect the emissive properties of the device.
It is therefore an object of the present invention to provide an OLED possessing higher brightness.
Another object of the present invention is to provide an OLED with higher power efficiency.
A further object of the present invention is to provide an OLED with an increased lifetime.
Yet another object of the present invention is to provide an OLED with a low heat output.
A further object of the present invention is to provide an OLED with increased light output utilizing approximately the same power as a single conventional light emitting device.
Yet another object of the present invention is to provide a transparent stackable OLED structure without requiring independent control of each of the stacked individual OLEDs.
An additional object of the present invention is to provide a transparent stacked OLED structure which draws no more current than a single OLED, but results in an increased brightness.
Yet a further object of the present invention is to provide a device with increased brightness over that of a single OLED, without loss of efficiency or loss of lifetime.
An additional object of the present invention is to provide the same brightness as a single OLED, but with increased efficiency and increased lifetime.
Additional benefits and advantages of the present invention will be apparent to those of ordinary skill in the art.
The present invention is directed to a light emitting device comprising a plurality of organic light emitting devices. The plurality of organic light emitting devices are arranged in a stack. The light emitting device further includes control means for controlling operation of each of the plurality of organic light emitting devices in the stack. The control means supplies the same current to each of the organic light emitting devices in the stack. The control means simultaneously supplies the same current to each of the plurality of the organic light emitting devices.
The plurality of organic light emitting devices includes at least two stacked organic light emitting devices. The stack of organic light emitting devices is formed on the substrate. The first organic light emitting device of the plurality of organic light emitting devices is located on the substrate. A second organic light emitting device of the plurality of organic light emitting devices is located on the first organic light emitting device.
The light emitting device may further include an insulator layer positioned between each of the organic light emitting devices.
Each of the organic light emitting devices includes a first conductor layer, an OLED layer, and a second conductor layer. The OLED layer is sandwiched between the first and second conductor layers. The thickness of the second conductor layer of the third organic light emitting device is greater than the thickness of the second conductor layers of the first and second organic light emitting devices.
The light emitting device according to the present invention has increased brightness capability. The light emitting device according to the present invention also has increased efficiency and lifetime.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only. The description is not considered to be restrictive of the invention as claimed.